opensecrets.org: Lobbying Database

Description:
Find data on expenditures of lobbying firms and lobbyists to Congress and other government agencies. Search by lobby firm or lobbyist name, industry (such as defense or agribusiness), issue (budget, trade, and others), or government agency. Data goes back to 1998. From the Center for Responsive Politics, "a non-partisan, non-profit research group ... that tracks money in politics, and its effect on elections and public policy."